JP4383316B2 - Magnetic recording medium and magnetic tape cartridge - Google Patents

Description

  The present invention relates to a coating type magnetic recording medium having excellent high recording density characteristics and few errors.

  Magnetic recording media have various uses such as audio tapes, video tapes, computer tapes, magnetic disks, and magnetic cards. Especially in the field of data backup tapes, as the capacity of hard disks to be backed up increases, 1 Magnetic tapes having a recording capacity of several hundred GB or more per roll have been commercialized. In the future, a large-capacity backup tape exceeding 1 TB has been proposed, and its high recording density is indispensable.

  In producing magnetic tapes corresponding to such high recording density, magnetic powder (hereinafter also referred to as magnetic particles) is made fine (hereinafter also referred to as fine powder) and high density in the coating film. Advanced techniques for filling, smoothing the coating, and thinning the magnetic layer are used.

  With regard to the improvement of magnetic powder, in order to cope with short wavelength recording, improvement of magnetic properties has been achieved along with the formation of fine particles, and acicular metal magnetic powder having an average particle diameter of 100 nm or less (Patent Document 1) A magnetic recording medium using a plate-shaped hexagonal ferrite magnetic powder (Patent Document 2) of 50 nm or less and a spherical or elliptical rare earth-iron nitride magnetic powder (Patent Document 3) of 50 nm or less has been proposed. Also, in order to prevent a decrease in output due to demagnetization during short wavelength recording, a higher coercive force has been achieved year by year.

  On the other hand, with respect to improvements in the manufacturing technology of magnetic recording media, the recording wavelength has become shorter with the recent increase in recording density, so the uppermost magnetic layer (when only one magnetic layer is provided) If the thickness of the magnetic layer is too large, the influence of self-demagnetization loss during recording / reproduction and the thickness loss due to the thickness of the magnetic layer, which has not been a significant problem in the past, is increased, and the output is increased. The problem of decreasing has grown. Therefore, it is necessary to reduce the thickness of the uppermost magnetic layer.

  When the thickness of the top magnetic layer is reduced, the effect of the weak magnetic flux leakage from the magnetic layer and the surface roughness of the nonmagnetic support is greatly reflected on the surface of the magnetic layer, and the surface properties of the magnetic layer are likely to deteriorate. There is a problem. In addition, when only a single magnetic layer is thinned, a method of reducing the solid content concentration of the magnetic coating or reducing the coating amount can be considered, but depending on these methods, defects during coating or magnetic powder There is a problem that the filling property is not improved and the strength of the coating film is weakened.

  For this reason, when the uppermost magnetic layer is thinned by improving the medium manufacturing technique, an undercoat layer (hereinafter also referred to as the lower layer) is provided between the nonmagnetic support and the magnetic layer, and the undercoat layer is wet. A so-called simultaneous multilayer coating method has been proposed in which the uppermost magnetic layer is coated while it is in a state (for example, Patent Document 4).

  In order to make the leakage flux from the magnetic layer extremely weak, in a system using these magnetic recording media, a high-sensitivity MR (magneto-resistance effect) type head is used as a reproducing head. . Since the MR head does not have an induction coil, the device noise is small, and an excellent C / N can be obtained by reducing the noise of the magnetic recording medium. However, this MR head is more prone to noise (thermal noise) due to the collision between the MR element and minute irregularities on the surface of the magnetic layer, which was not a problem with the magnetic induction type. Need to control.

JP 2004-5792 A JP 2004-30828 A WO03 / 079332A1 brochure JP-A-5-197946

  In order to provide both high recording density characteristics and durability to the magnetic layer thinned to support short wavelength recording as described above, smoothing the coating film and supplying lubricant from the lower layer In addition, it is important to control the shape of the coating film surface with various abrasives and carbon black contained in the magnetic layer.

  However, in the magnetic recording media disclosed in Patent Document 1 to Patent Document 3, the shape control of the coating film surface is insufficient, and the high recording density characteristics and durability are sufficiently achieved by using the fine particle magnetic powder. It was difficult to be.

  The present invention has been made in order to achieve the above-mentioned problems. For example, the magnetic tape is excellent in high recording density characteristics capable of corresponding to a recording capacity of 1 TB or more per tape roll and highly reliable in terms of durability. The purpose is to provide.

  As a result of intensive studies, the inventors of the present invention have the following configuration in a magnetic recording medium having a magnetic layer containing at least magnetic powder and carbon black on a nonmagnetic support in order to achieve the above object. As a result, the inventors have found that the above object can be achieved, and have accomplished the present invention.

That is, the present invention provides a magnetic recording medium having a magnetic layer containing at least a magnetic powder having an average particle diameter of 5 nm to 30 nm and carbon black on a nonmagnetic support, wherein the thickness of the magnetic layer is less than 100 nm. The carbon black has an average particle diameter of less than 100 nm, the magnetic powder has an axial ratio or plate-like ratio of 1 or more and less than 3, the carbon black has an average particle diameter of Dc, and the magnetic layer has a thickness of The present invention relates to a magnetic recording medium satisfying a relationship of 0.5 ≦ Dc / Dm ≦ 1.0 when Dm .

  Since the magnetic layer is thinned and the average particle diameter of carbon black with respect to the shape of the magnetic powder and the thickness of the magnetic layer is controlled within a preferable range, a magnetic recording medium having both high recording density characteristics and durability can be obtained. It is done.

  In order to improve the self-demagnetization loss and the reproduction waveform resolution during short wavelength recording, it is preferable to reduce the thickness of the uppermost magnetic layer. The thickness of the magnetic layer is preferably 10 nm or more and less than 100 nm, and more preferably 80 nm or less. If the thickness of the magnetic layer is less than 10 nm, the output obtained may be too small or it may be difficult to apply a uniform magnetic layer. If it exceeds 100 nm, self-demagnetization and thickness loss become too large, and short wavelength recording and reproduction This is because the characteristics deteriorate.

  In a recording / reproducing apparatus that uses an MR head as a reproducing head, it is a big problem to reduce the noise of the magnetic recording medium. For this purpose, it is necessary to increase the number of magnetic powder particles contained in the unit volume of the coating film of the magnetic layer as much as possible. For this purpose, it is preferable to increase the number of magnetic powder particles contained in a unit volume by reducing the particle size of the magnetic powder, reducing the particle volume, and increasing the packing property of the magnetic powder particles.

  Conventionally, the shape of the magnetic powder has been generally needle-like or plate-like, but in recent years, a spherical one has also been proposed (Patent Document 3). When forming a magnetic coating film of a magnetic recording medium, a step of orienting magnetic powder in the recording direction is generally provided, thereby increasing the reproduction output. Even if the magnetic powder is oriented in the orientation step, it is difficult to completely orient the magnetic powder, and a certain percentage of the magnetic powder remains without being oriented. When magnetic powder having a shape anisotropy such as a needle shape or a plate shape is used, the unoriented magnetic powder lowers the filling property, which may hinder the noise reduction described above. In the case of spherical magnetic powder, even if there is unoriented magnetic powder, the filling structure is not disturbed, so that a coating film with a high filling degree can be obtained.

  According to the study by the present inventors, from the above viewpoint, even in the case of acicular magnetic powder or plate-like magnetic powder, the acicular ratio (major axis length / minor axis length) or plate ratio (plate diameter / plate thickness) The smaller is preferable, and when it approaches 1, the same effect as the granular powder can be obtained. As a result of the study by the present inventors, the acicular ratio is preferably less than 3 in the acicular magnetic powder such as the ferromagnetic iron-based metal magnetic powder, and in the platy magnetic powder such as the hexagonal barium ferrite magnetic powder, The shape ratio was preferably less than 3, more preferably less than 2, more preferably 1.5 or less, and most preferably less than 1.5. In the present invention, the shape anisotropic magnetic powder having a small acicular ratio or plate ratio and a granular magnetic powder having an axial ratio of less than 2, more preferably 1.5 or less, and even more preferably less than 1.5. Hereinafter referred to as substantially granular magnetic powder.

  Further, as described above, when the magnetic layer is thinned, the control of the surface roughness becomes more important than ever. Conventionally, carbon black has been used for the magnetic layer in order to improve conductivity and runnability.

  The present inventors examined the behavior of carbon black particles when the magnetic layer was thinned and the magnetic layer thickness approached the particle size of carbon black. Because the specific gravity is small compared to the powder particles, it tends to protrude to the surface of the magnetic layer more than other non-magnetic powder particles contained in the magnetic layer, and the thickness of the magnetic layer is conventionally larger than the particle size of carbon black. However, the carbon black particle size, which was not considered as a problem, greatly affects the surface shape of the magnetic layer, as compared with other nonmagnetic powders, as the magnetic layer thickness decreases. I found out.

Furthermore, when the thickness of the magnetic layer is Dm and the average particle diameter of the carbon black contained in the magnetic layer is Dc, if Dm and Dc satisfy the following relationship, the high density recording characteristics and durability are excellent. The inventors have found that a magnetic recording medium with low thermal noise can be obtained. That is, Dm is less than 100 nm, and it is preferable that Dm and Dc satisfy the relationship of 0.5 ≦ Dc / Dm ≦ 1.0. When Dc / Dm exceeds 1.0, the protrusions due to the carbon black particles are increased, the spacing with the MR head is increased, the output is decreased, and the thermal noise is increased. When Dc / Dm is less than 0.5, the effect of reducing the friction of the magnetic layer by the carbon black particles is lowered, and the friction is increased or the running durability is lowered.
The average particle size of carbon black here is the number obtained by observing the cross section of the magnetic layer at a magnification of 200,000 using a scanning electron microscope (SEM) and measuring 50 primary particle sizes of carbon black. Average particle size.

Hereinafter, other components of the present invention will be described in more detail.
<Magnetic layer>
The thickness of the magnetic layer is preferably less than 100 nm, and more preferably 10 nm or more and less than 100 nm. This is because if it exceeds 100 nm, the self-demagnetization and the thickness loss become too large, and the short wavelength recording / reproducing characteristics deteriorate. On the other hand, if the thickness is less than 10 nm, the output obtained may be small or it may be difficult to apply a uniform magnetic layer.

  The coercive force of the magnetic layer is preferably 160 to 400 kA / m, more preferably 200 to 350 kA / m, and further preferably 220 to 320 kA / m. This range is preferable because if the recording wavelength is shorter than 160 kA / m, the output is reduced due to demagnetization, and if it exceeds 400 kA / m, recording by the magnetic head may be difficult.

  The binder (binder resin) used for the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, A combination of a polyurethane resin and at least one selected from vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resins, and cellulose resins such as nitrocellulose. and so on. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.

  Examples of the polyurethane resin include polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, polyester polycarbonate polyurethane resin, and the like.

The binder resin has —COOH, —SO ₃ M, —OSO ₃ M, —P═O (OM) ₃ , —O—P═O (OM) ₂ [in these formulas, M is hydrogen. Represents an atom, an alkali metal base or an amine salt], —OH, —NR ₁ R ₂ , —N ⁺ R ₃ R ₄ R ₅ [in these formulas, R ₁ , R ₂ , R ₃ , R ₄ , R _5] Represents a hydrogen or hydrocarbon group], and a polymer such as a urethane resin having an epoxy group or the like is particularly preferable.

The reason why such a binder resin is preferable is that dispersibility of magnetic powder and the like is improved. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  In the magnetic layer, the binder (binder resin) is usually used in a ratio of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, with respect to 100 parts by weight of the magnetic powder. In particular, it is most preferable to use a composite of 5-30 parts by weight of vinyl chloride resin and 2-20 parts by weight of polyurethane resin as the binder resin.

Moreover, it is preferable to use together with said binder resin the thermosetting crosslinking agent couple | bonded with the functional group etc. which are contained in binder resin, and bridge | crosslinks.
Various crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. The polyisocyanate is preferably used.
These crosslinking agents are generally used in a proportion of 1 to 30 parts by weight, preferably 5 to 20 parts by weight, per 100 parts by weight of the binder resin. When a magnetic layer is applied wet-on-wet on the undercoat layer, a certain amount of polyisocyanate is diffused and supplied from the undercoat paint, so that the magnetic layer is crosslinked to some extent without using polyisocyanate.

  Instead of the above-described thermosetting binder resin, a radiation curable resin may be used. As the radiation curable resin, those obtained by acrylic modification of the above thermosetting resin to give a radiation sensitive double bond, acrylic monomers, and acrylic oligomers are used.

  The average particle size of the magnetic powder contained in the magnetic layer is preferably in the range of 5 nm to 30 nm, and more preferably 10 nm or more. Moreover, 25 nm or less is more preferable, and 20 nm or less is further more preferable. This range is preferable because if the average particle size is less than 5 nm, the surface energy of the particles may increase and dispersion may become difficult, and if the average particle size exceeds 30 nm, noise tends to increase. .

  As such magnetic powder, ferromagnetic iron-based metal magnetic powder, iron nitride-based magnetic powder, hexagonal Ba-ferrite magnetic powder and the like are preferably used.

  The ferromagnetic iron-based metal magnetic powder may contain transition metals such as Mn, Zn, Ni, Cu, and Co as an alloy. Among these, Co and Ni are preferable, and Co is particularly preferable because it can improve saturation magnetization most. As a quantity of said transition metal element, it is preferable to set it as 5-50 atomic% with respect to iron, and it is more preferable to set it as 10-30 atomic%.

  Further, at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium and the like may be included. Among these, when cerium, neodymium and samarium, terbium, and yttrium are used, a high coercive force can be obtained, which is preferable. The amount of the rare earth element is 0.2 to 20 atomic%, preferably 0.3 to 15 atomic%, and more preferably 0.5 to 10 atomic% with respect to iron.

  The ferromagnetic iron-based metallic magnetic powder is usually needle-shaped, spindle-shaped, or rice-grained, but preferably has an average particle diameter (major axis diameter) of 10 nm to 30 nm. This is because if the average particle diameter is less than 10 nm, the coercive force is out of the preferred range, the specific surface area is increased, the dispersion becomes unstable, and the preferred recording / reproducing characteristics may not be obtained. When the average particle diameter exceeds 30 nm, the particle noise based on the particle size increases. The axial ratio (major axis diameter / minor axis diameter) of the ferromagnetic iron-based metal magnetic powder is preferably 1 or more and less than 3. This range is preferred because the degree of filling of the coating film does not decrease when the magnetic field is oriented.

  Known iron nitride magnetic powders can be used. As the shape, a polyhedral shape such as a spherical shape, a substantially spherical shape, an elliptical shape, a substantially elliptical shape, a cubic shape, or a substantially polyhedral shape can be used. The average particle size is preferably 30 nm or less, and more preferably 20 nm or less. The axial ratio of the magnetic powder is preferably 1 or more and less than 2, more preferably 1.5 or less, and even more preferably less than 1.5.

Among them, the outer layer portion is mainly composed of at least one element such as rare earth elements, aluminum, silicon, zirconium, titanium, etc. whose oxide is not reduced by hydrogen reduction at 600 ° C. or less (particularly, rare earth elements, aluminum, silicon). Iron-based magnetism containing iron or iron-based transition metal nitrides (particularly, Fe ₁₆ N ₂ or a part of Fe substituted with a transition metal) in the core part The powder is preferably used because it easily obtains a coercive force of 200 kA / m or more.

The coercive force of the ferromagnetic iron-based metal magnetic powder or the iron nitride-based magnetic powder is preferably 160 to 400 kA / m, and more preferably 200 to 350 kA / m. Saturation magnetization is preferably a ^{60~200A · m 2 / kg (60~200emu} / g), more preferably from ^{80~180A · m 2 / kg (80~180emu} / g).

Further, the BET specific surface area of these ferromagnetic powders is preferably 35 m ² / g or more, more preferably 40 m ² / g or more, and most preferably 50 m ² / g or more. Usually, it is good that it is 100 m ² / g or less.

The coercive force of the hexagonal Ba-ferrite magnetic powder is preferably 160 to 400 kA / m, and more preferably 200 to 350 kA / m. The saturation magnetization is preferably 40 to 60 A · m ² / kg (40 to 60 emu / g).

  The particle size (size in the plate surface direction) of the hexagonal Ba-ferrite magnetic powder is preferably 10 nm or more and less than 30 nm. Moreover, 25 nm or less is more preferable, and 20 nm or less is further more preferable. When the particle size is less than 10 nm, the surface energy of the particles increases, so dispersion in the paint may be difficult. When the particle size exceeds 30 nm, particle noise based on the size of the particles tends to increase. Because.

Further, the plate ratio (plate diameter / plate thickness) of the hexagonal Ba-ferrite magnetic powder is preferably 1 or more and less than 3, more preferably 1 or more and 2 or less, further preferably 1 or more and 1.5 or less. Most preferred is less than 1.5. The hexagonal Ba-ferrite magnetic powder preferably has a BET specific surface area of 1 to 100 m ² / g.

  Further, in order to improve the dispersibility of the magnetic powder, the above-described ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder or hexagonal Ba-ferrite magnetic powder is converted into an Al, Si, P, Y, Zr compound or an oxidation thereof. It may be used after being surface-treated with an object.

  The magnetic powder contained in the magnetic layer is more preferably an iron nitride-based magnetic powder or hexagonal Ba-ferrite magnetic powder that can obtain a particularly large coercive force among the above-mentioned preferable magnetic powders. The iron nitride magnetic powder is most preferable.

  Note that the magnetic characteristics of these magnetic powders all mean values measured with an external magnetic field 1273.3 kA / m (16 kOe) using a sample vibration magnetometer.

  The average particle diameter of these magnetic powders is the maximum diameter of each particle (major axis diameter for needle-like powder, plate diameter for plate-like powder) from a photograph taken at 200,000 times with a scanning electron microscope (SEM). Is actually obtained and obtained from the number average value of 50 pieces.

  In the magnetic recording medium of the present invention, conventionally known carbon black is added to the magnetic layer in order to improve conductivity and surface lubricity. As carbon black, acetylene black, furnace black, thermal black, etc. can be used.

  As described above, carbon black satisfies the relationship of 0.5 ≦ Dc / Dm ≦ 1.0 when the average particle size of carbon black is Dc and the thickness of the magnetic layer is Dm (less than 100 nm). Is used. If necessary, carbon black having an average particle size smaller than that of carbon black satisfying the above relationship may be used.

  Moreover, you may add nonmagnetic powders other than carbon black to a magnetic layer as needed. The nonmagnetic powder other than carbon black contained in the magnetic layer preferably has an average particle size of less than 150 nm, more preferably less than 100 nm, and most preferably less than the thickness of the magnetic layer. The non-magnetic powder is preferably α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, and dioxide. Those having a Mohs hardness of 6 or more, such as silicon and boron nitride, are used alone or in combination.

  In addition, as long as the effect of improving durability is obtained, metal salt powder such as calcium carbonate and barium sulfate, organic powder insoluble in organic solvents such as benzoguanamine, crosslinked polystyrene, polyethylene, silicon resin, polytetrafluoroethylene, etc. Conventionally known non-magnetic powders can be widely used.

  In the magnetic recording medium of the present invention, the addition amount of the nonmagnetic powder may be appropriately selected according to the required specifications of the durability of the magnetic recording medium and the head polishing amount. It is preferably 20% by weight.

<Non-magnetic support>
Although the thickness of a magnetic support body changes with uses, a 1.5-11.0 micrometer thing is used normally. More preferably, it is 2.0-7.0 micrometers, Most preferably, it is 2.0-6.0 micrometers. Nonmagnetic supports with a thickness in this range are used when film thickness is less than 1.5 μm, and the strength of the tape decreases, and when it exceeds 11.0 μm, the total thickness of the tape increases, and one roll of tape. This is because the recording capacity per unit becomes small.

Longitudinal Young's modulus of the non-magnetic support is preferably 5.8GPa (590kg / mm ²⁾ or more, more preferably at least ^{7.1GPa (720kg / mm 2),} 7.8GPa (800kg / mm 2) or higher Most preferred. The longitudinal Young's modulus of the non-magnetic support is preferably 5.8 GPa (590 kg / mm ² ) or more. If the Young's modulus in the longitudinal direction is less than 5.8 GPa (590 kg / mm ² ), the tape running becomes unstable. Because.

In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in the range of 0.60 to 0.80, and more preferably in the range of 0.65 to 0.75. . The above range is good when it is less than 0.60 or exceeds 0.80, but the mechanism is currently unknown, but the output variation (flatness) between the entrance side and the exit side of the track of the magnetic head This is because of the increase.

  This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70. Further, in the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.70 to 1.30, although the reason is not clear.

The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 ⁻⁶ , and the humidity expansion coefficient is preferably 0 to 10 × 10 ⁻⁶ . The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate may increase.

  Examples of the non-magnetic support that satisfies all the above-mentioned properties include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film.

<Undercoat layer>
In the present invention, since the thickness of the magnetic layer is as thin as less than 100 nm, it is preferable to provide an undercoat layer in order to increase the smoothness of the magnetic layer and improve the short wavelength recording characteristics.

  The thickness of the undercoat layer is preferably 0.2 μm or more and less than 1.0 μm, and more preferably 0.8 μm or less. This range is preferably less than 0.2 μm, the effect of reducing the thickness unevenness of the magnetic layer, the effect of improving the durability is reduced, and when it is 1.0 μm or more, the total thickness of the magnetic tape becomes too thick, This is because the recording capacity per tape roll is reduced.

  Nonmagnetic powders used for the undercoat layer include titanium oxide, iron oxide, and aluminum oxide. Iron oxide alone or a mixed system of iron oxide and aluminum oxide is preferably used. The particle shape of the non-magnetic powder may be spherical, plate-like, needle-like, or spindle-like, but in the case of needle-like or spindle-like, the major axis length is usually 50 to 200 nm and the minor axis length is 5 to 100 nm. Is preferred. In the case of a granular shape, a particle size of 5 to 200 nm, more preferably 5 to 100 nm is used.

  In many cases, such non-magnetic powder is mainly supplemented with carbon black having a particle diameter of 0.01 to 0.1 μm and acicular or granular aluminum oxide having the above-mentioned particle diameter as necessary. In order to apply the undercoat layer smoothly and with little thickness unevenness, it is particularly preferable to use nonmagnetic powder and carbon black having a sharp particle size distribution.

  In order to reduce the temperature / humidity expansion coefficient of the magnetic recording medium and improve the smoothness of the upper magnetic layer, it is preferable to add a nonmagnetic plate-like powder having an average particle diameter of 10 to 100 nm to the undercoat layer. As a component of the nonmagnetic plate-like powder, a rare earth element such as cerium, an oxide or a complex oxide of an element such as zirconium, silicon, titanium, manganese, or iron is used.

For the purpose of improving the conductivity, a plate-like carbonaceous powder such as graphite having an average particle size of 10 to 100 nm or a plate-like ITO (indium, tin composite oxide) powder having an average particle size of 10 to 100 nm may be added. . By adding the nonmagnetic plate powder, the film thickness uniformity, surface smoothness, rigidity, and dimensional stability are improved. In addition, as a binder (binder resin) used for an undercoat layer, the thing similar to the below-mentioned magnetic layer can be used.
An undercoat layer containing magnetic powder is not excluded.

<Lubricant>
The magnetic layer and the undercoat layer preferably contain 0.5 to 3.0% by weight of fatty acid amide with respect to the total powder contained in the magnetic layer and the undercoat layer. It is preferable to contain -5.0 weight% of higher fatty acid, and it is further preferable to contain 0.2-3.0 weight% of higher fatty acid ester.

  It is preferable to add the fatty acid amide within the above range. When the amount is less than 0.5% by weight, direct contact at the head / magnetic layer interface is likely to occur, and the effect of preventing seizure is small. This is because defects such as dropout may occur. Also, the addition of higher fatty acids within the above range is preferred because if the amount is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5.0% by weight, the primer layer may be plasticized and the toughness may be lost. Because there is. Furthermore, the addition of a higher fatty acid ester within the above range is preferable because if the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, the amount transferred to the magnetic layer is too large. This is because side effects such as sticking of the head may occur.

  The higher fatty acid is preferably a fatty acid having 10 or more carbon atoms, and the higher fatty acid ester is preferably an ester of the above higher fatty acid. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

  In addition, the mutual movement of the lubricant in the magnetic layer and the lubricant in the undercoat layer is not excluded, and when the lubricant is contained in the undercoat layer, the magnetic layer may not contain the lubricant. On the contrary, when the effect is manifested only by being included in the magnetic layer, it may not be included in the undercoat layer.

  In addition, in order to include a lubricant in the undercoat layer and the magnetic layer, in addition to the method of adding the lubricant to the coating material for forming each layer, the lubricant or lubricant is included after the formation of the undercoat layer and the magnetic layer. Various methods such as a method of dipping or spraying the solution can be employed.

<Dispersant>
The nonmagnetic powder, carbon black, and magnetic powder contained in the undercoat layer and magnetic layer can be surface-treated with an appropriate dispersant in order to improve dispersibility with the binder (binder resin). Moreover, you may add an appropriate dispersing agent in the coating material for forming the undercoat layer and magnetic layer containing said each powder. As the dispersant, a phosphoric acid-based dispersant, a carboxylic acid-based dispersant, an amine-based dispersant, a chelating agent, various silane coupling agents, and the like are preferably used. These dispersants are preferably blended after the kneading pretreatment step, the kneading step and the initial dispersion step. Examples of phosphate dispersants include alkyl phosphates such as monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, and diethyl phosphate, and aromatic phosphates such as phenylphosphonic acid and monooctylphenylphosphonic acid. As commercial products, “GARFAC RS410” manufactured by Toho Chemical Co., Ltd., “JP-502”, “JP-504”, “JP-508” manufactured by Johoku Chemical Industry Co., Ltd., and the like can be used. Moreover, as a carboxylic acid type | system | group dispersing agent, a C12-C18 fatty acid, specifically, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid Linoleic acid, linolenic acid, stearic acid and the like are used. Also, a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, an amide of the fatty acid, an ester of the fatty acid or a compound containing fluorine in the fatty acid, a polyalkylene oxide alkyl phosphate ester, lecithin, a trialkyl polyolefinoxy Quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphate, copper phthalocyanine, benzoic acid, phthalic acid, tetracarboxyl naphthalene, dicarboxyl naphthalene And fatty acids having 12 to 22 carbon atoms. Examples of the amine dispersant include aliphatic amines having 8 to 22 carbon atoms, aromatic amines, alkanolamines, and alkoxyalkylamines. Further, examples of chelating agents include 1,10-phenanthroline, EDTA, dimethylglyoxime, acetylacetone, glycine, dithiazone, nitrilotriacetic acid and the like. These may be used alone or in combination.

  The dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder in any layer.

<Back coat layer>
A back layer may be provided on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support constituting the magnetic recording medium of the present invention for the purpose of improving running performance. it can. The back layer is formed by vapor deposition, sputtering, CVD, or coating, and a back coat layer mainly composed of carbon black and a binder resin is generally used.

  Since the magnetic signal of the magnetic layer may be disturbed if the backcoat layer is magnetic, the backcoat layer is usually nonmagnetic. The thickness of the back coat layer is preferably 0.2 to 0.8 μm. This range is good because if the thickness is less than 0.2 μm, the effect of improving running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the recording capacity per roll becomes small. Moreover, 3-8 nm is preferable and, as for centerline average surface roughness Ra, 4-7 nm is more preferable.

  As the carbon black to be included in the back coat layer, acetylene black, furnace black, thermal black and the like can be used. Usually, it is desirable to use a small particle size carbon black and a large particle size carbon black in combination. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder.

  As the small particle size carbon black, those having an average particle size of 5 to 200 nm are preferable, and those having an average particle size of 10 to 100 nm are more preferable. This range is preferable, if the average particle size is too small, it is difficult to disperse the carbon black, and if the average particle size is too large, it is necessary to add a large amount of carbon black, in each case the surface becomes rough, This is because it causes a back-off (embossing) to the magnetic layer.

  Moreover, when the large particle diameter carbon black is 5 to 15% by weight of the small particle diameter carbon black and the large particle diameter carbon black having an average particle diameter of 200 to 400 nm is used, the surface is not roughened, and the running performance is improved. growing.

  A nonmagnetic plate-like powder having an average particle diameter of 10 to 100 nm can be added to the backcoat layer for the purpose of improving strength, temperature / humidity dimensional stability, and the like.

  The component of the nonmagnetic plate-like powder is not limited to aluminum oxide, and rare earth elements such as cerium, and oxides or composite oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used. For the purpose of improving conductivity, a plate-like carbonaceous powder having an average particle size of 10 to 100 nm, a plate-like ITO powder having an average particle size of 10 to 100 nm, or the like may be added.

  Moreover, you may add the granular iron oxide powder whose average particle diameter is 0.1-0.6 micrometer as needed. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the total inorganic powder in the backcoat layer. Moreover, it is preferable to add alumina having an average particle size of 0.1 to 0.6 μm because durability is further improved.

  In the back coat layer, the same resin as that used for the magnetic layer and the undercoat layer can be used as a binder (binder resin). Among these, in order to reduce the coefficient of friction and improve the running performance, it is desirable to use a cellulose resin and a polyurethane resin in combination.

  The amount of the binder resin used is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight, based on 100 parts by weight of the total amount of carbon black and the inorganic nonmagnetic powder. Preferably it is 70-110 weight part.

  If the binder resin is too small, the strength of the backcoat layer becomes insufficient, and if it is excessive, the friction coefficient tends to be high. The binder resin is most preferably 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin.

  Moreover, it is preferable to use a crosslinking agent such as a polyisocyanate compound in order to cure the binder resin. The usage-amount of a crosslinking agent is 10-50 weight part normally with respect to 100 weight part of binder resin, Preferably it is 10-35 weight part, More preferably, it is 10-30 weight part. If the amount of the crosslinking agent used is too small, the coating strength of the backcoat layer tends to be weak, and if it is too large, the dynamic friction coefficient with respect to a guide roller (material is, for example, SUS304) provided in the running system of the tape drive is large. Become. In addition, the electron beam curable resin similar to the magnetic layer and the undercoat layer can also be used as a crosslinking agent.

  When the thickness of the undercoat layer is 0.5 μm or less, the lubricant component supplied from the undercoat layer may be insufficient. In that case, it is desirable to include a lubricant in the backcoat layer and supply the lubricant from the backcoat layer to the surface on the magnetic layer side. The type of lubricant used is the same as that used for the magnetic layer and the undercoat layer. As the addition amount, 0.5 to 3.0% by weight of fatty acid amide, 0.2 to 3.0% by weight of higher fatty acid ester, 0.5 to 5% with respect to the total nonmagnetic powder in the backcoat layer. It is preferable to contain 0.0% by weight of higher fatty acid.

<Organic solvent>
Examples of organic solvents used in magnetic paints, undercoat paints, and backcoat paints include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetates such as ethyl acetate and butyl acetate. System solvents and the like. These organic solvents are used alone or in combination, and further mixed with toluene.

  EXAMPLES The present invention will be described in detail below by examples, but the present invention is not limited to these. In addition, the part of an Example and a comparative example shows a weight part. Moreover, the average particle diameter of an Example and a comparative example shows a number average particle diameter.

Example 1:
<Undercoat paint component>
(1)
・ Nonmagnetic plate-like iron oxide powder (average particle size: 50 nm) 76 parts ・ Carbon black (average particle size: 25 nm) 24 parts ・ Stearic acid 2.0 parts ・ Vinyl chloride-hydroxypropyl acrylate copolymer 8.8 parts (Contained -SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Stearic acid 1 part ・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts

《Magnetic paint component》
(1) Kneading process / magnetic powder (YN-Fe) 100 parts (Y / Fe: 5.5 at%,
N / Fe: 11.9 at%
σs: 103 A · m ² / kg (103 emu / g),
Hc: 211.0 kA / m (2650 Oe),
(Average particle diameter: 17 nm, axial ratio: 1.2)
-13 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin (PU) 4.5 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)
・ Particulate alumina powder (average particle size: 40 nm) 10 parts ・ Methyl acid phosphate (MAP) 2 parts ・ Carbon black 3 parts (average particle size: 75 nm, oil absorption 72 ml / 100 g)
-Tetrahydrofuran (THF) 20 parts-Methyl ethyl ketone / cyclohexanone (MEK / A) 9 parts (2) Dilution step-Palmitic acid amide (PA) 1.5 parts-N-butyl stearate (SB) 1 part-Methyl ethyl ketone / cyclohexanone ( MEK / A) 350 parts (3) Compounding process ・ Polyisocyanate 1.5 parts ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts

  After kneading (1) with a batch kneader in the above-mentioned undercoat paint component, add (2) and stir, and then disperse with a sand mill with a residence time of 60 minutes. Add (3) to this and stir and filter After that, an undercoat paint (undercoat layer paint) was obtained.

  Separately, (1) kneading step components are mixed at high speed in advance in the above magnetic coating components, the mixed powder is kneaded with a continuous biaxial kneader, and (2) dilution step components are added and continuously. Dilution was performed in at least two stages using a formula biaxial kneader, and dispersion was performed with a sand mill with a residence time of 45 minutes. To this, (3) ingredients of the blending step were added, stirred and filtered to obtain a magnetic paint.

  On the nonmagnetic support (base film) made of an aromatic polyamide film (thickness: 3.9 μm, MD = 11 GPa, MD / TD = 0.7, trade name: Miktron, Toray Industries, Inc.) , Dried, and coated so that the thickness after calendering becomes 0.9 μm, and the magnetic coating is further coated on the undercoat layer with a magnetic layer having a thickness of 0. 0 after magnetic field orientation treatment, drying and calendering treatment. The coating was applied wet-on-wet with an extrusion coater to a thickness of 09 μm, and after magnetic field orientation treatment, it was dried using a dryer and far infrared rays to obtain a magnetic sheet.

《Paint component for back coat layer》
Carbon black (average particle size: 25 nm) 80 parts Carbon black (average particle size: 350 nm) 10 parts Nonmagnetic plate-like iron oxide powder (average particle size: 50 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin ( -SO ₃ Na group-containing) 30 parts ・ Cyclohexanone 260 parts ・ Toluene 260 parts ・ Methyl ethyl ketone 525 parts

  After dispersing the coating component for the backcoat layer with a sand mill with a residence time of 45 minutes, after adding 15 parts of polyisocyanate to adjust the coating for the backcoat layer and filtering, on the opposite side of the magnetic layer of the magnetic sheet prepared above, It was applied and dried so that the thickness after drying and calendering was 0.5 μm.

  The magnetic sheet thus obtained was mirror-finished under the conditions of a temperature of 100 ° C. and a linear pressure of 196 kN / m with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound around the core at 70 ° C. at 72 ° C. Time-aging was performed to obtain a magnetic sheet with a back layer.

  The magnetic sheet was cut into ½ inch width by a slit machine. A slit machine (an apparatus for cutting a magnetic tape original into a magnetic tape having a predetermined width) was used in which various constituent elements were improved as follows. A tension cut roller was provided in the web path from the unwinding raw fabric to the slit blade group, this tension cut roller was a suction type, and the suction part was a mesh suction in which a porous metal was embedded. A direct drive directly connected to a motor without a mechanism for transmitting power to the blade drive unit was used.

  The magnetic tape obtained as described above was assembled in a cartridge to produce a computer tape.

Example 2:
Barium magnetic powder (Ba-Fe) (σs: 51 A · m ² / kg (51 emu / g), Hc: 161.5 kA / m (2029 Oe), average particle diameter: 25 nm, plate ratio: 2. A computer tape of Example 2 was produced in the same manner as Example 1 except for changing to 7).

Example 3:
The magnetic powder was made of iron-based magnetic powder (Co—Fe) (σs: 92 A · m ² / kg (92 emu / g), Hc: 111.4 kA / m (1400 Oe), average particle size: 30 nm, and axial ratio: 2. A computer tape of Example 3 was produced in the same manner as in Example 1 except that the method was changed to 8).

Comparative Example 1:
A computer tape of Comparative Example 1 was produced in the same manner as in Example 1 except that the carbon black contained in the magnetic paint was changed to one having an average particle size of 100 nm and an oil absorption of 68 ml / 100 g.

Comparative Example 2:
A computer tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the carbon black contained in the magnetic paint was changed to one having an average particle size of 40 nm and an oil absorption of 114 ml / 100 g.

Comparative Example 3:
A computer tape of Comparative Example 3 was produced in the same manner as in Example 1 except that the thickness of the magnetic layer was changed to 100 nm.

Comparative Example 4:
Barium magnetic powder (Ba-Fe) (σs: 52 A · m ² / kg (52 emu / g), Hc: 160.8 kA / m (2020 Oe), average particle size: 25 nm, plate ratio: 3. A computer tape of Comparative Example 4 was produced in the same manner as in Example 1 except that the procedure was changed to 2).

Comparative Example 5:
The magnetic powder was made of iron-based magnetic powder (Co—Fe) (σs: 88 A · m ² / kg (88 emu / g), Hc: 114.6 kA / m (1440 Oe), average particle size: 30 nm, and axial ratio: 3. A computer tape of Example 3 was produced in the same manner as in Example 1 except that the procedure was changed to 5).

Comparative Example 6:
The computer of Comparative Example 6 is the same as Example 1 except that the average particle size of the magnetic powder is 20 nm and the carbon black to be included in the magnetic paint is changed to one having an average particle size of 100 nm and an oil absorption of 68 ml / 100 g. A tape was prepared.

The evaluation method was performed as follows.
<C / N measurement>
A drum tester was used for measuring the electromagnetic conversion characteristics of the tape. The drum tester was equipped with an electromagnetic induction head (track width 25 μm, gap 0.2 μm) and an MR head (track width 8 μm), and recording was performed with the induction head and reproduction was performed with the MR head. Both heads are installed at different locations with respect to the rotating drum, and tracking can be adjusted by operating both heads in the vertical direction. An appropriate amount of the magnetic tape was drawn out from the state of being wound in the cartridge and discarded, and further 60 cm was cut, further processed into a width of 4 mm, and wound around the outer periphery of the rotating drum.
For the output and noise, a rectangular wave was input to the recording current / current generator by a function generator, a signal having a wavelength of 0.2 μm was written, the output of the MR head was amplified by a preamplifier, and then read into a spectrum analyzer. The carrier value of 0.2 μm was defined as the medium output C.

  Further, when a rectangular wave of 0.2 μm was written, an integrated value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.2 μm or more was used as the noise value N. Furthermore, the ratio of both was taken as C / N, and the relative value with the value of the tape of Comparative Example 6 was determined.

<Error rate>
Using a Quantum DLT7000 drive, run the entire track for 300 hours continuously in a room temperature environment, read the error information output by the drive via the RS-232C interface, and evaluate it as the number of errors per MB of recording capacity did.

<Magnetic layer thickness>
The sample magnetic recording medium was filled with resin, and the cross section in the thickness direction was cut out in the longitudinal direction of the tape with a focused ion beam processing apparatus, and the cross section was divided into 10 fields with a scanning electron microscope (SEM) at a magnification of 100,000. A photograph is taken to frame the magnetic layer surface and the magnetic layer-undercoat layer interface. Next, arbitrary five locations where no nonmagnetic powder is applied to the interface are selected per field of view of the photograph, and the distance between the bordered lines is measured as the thickness of the magnetic layer. The same measurement was performed for 10 fields of view of the photograph, and these were averaged to obtain the magnetic layer thickness.

<Carbon black particle size>
Except that the shooting magnification was set to 200,000 times, the required number of magnetic layer cross-sections were photographed in the same manner as in the case of obtaining the magnetic layer thickness described above, and the magnetic layer in the photographic field was set to 0.5 in the longitudinal direction. Each of the 5 μm lengths is divided and the outer shape of the primary particle having the largest particle diameter is outlined among the carbon black in the magnetic layer of each division. Carbon black usually has a primary particle as an isolated particle and a case where the primary particle forms a chain-connected structure. The outline is trimmed and the maximum of the outline is measured as the particle size. The same measurement was performed for 50 carbon blacks, and the number average value thereof was defined as the average particle size of the carbon black.

<Particle size and axial ratio of magnetic powder>
Except that the photographing magnification was set to 200,000 times, the same number of magnetic layer cross-sections were photographed as in the case of obtaining the magnetic layer thickness described above, and the particle size of the magnetic powder contained in the magnetic layer and Measure the axial ratio. The magnetic powder has a very small particle size and axial ratio distribution, so it is only necessary to measure the particle diameter and axial ratio of typical magnetic powder particles. For the powder particles, the particle diameter and axial ratio of each particle were measured, and the number average value of these 50 particles was taken as the average particle diameter and average axial ratio of the magnetic powder.

  Table 1 shows the evaluation results of each computer tape. As is apparent from the table, the computer tapes of Examples 1 to 3 according to the present invention have better C / N than the computer tapes of Comparative Examples 1 to 6 that do not satisfy Claim 1, Durability is also great.

  Next, the critical significance of various numerical values of the present invention will be clarified with reference to FIGS. First, FIG. 1 shows the relationship between the value of Dc / Dm and C / N. The experiment was conducted by changing the average particle diameter of carbon black in the range of 25 to 100 nm and the magnetic layer thickness in the range of 35 to 100 nm with Example 1 as the basic composition. The C / N value (dB) of the obtained computer tape is shown with each point. As is apparent from the figure, it can be seen that the C / N ratio decreases when the area is higher than the line (shown by a solid line) where Dc / Dm is 1 in the figure. It can also be seen that C / N decreases when the thickness of the magnetic layer is 100 nm or more.

  FIG. 2 shows the relationship between the value of Dc / Dm and the error rate (ER) after the durability running test. The experiment was conducted by changing the average particle diameter of carbon black in the range of 25 to 100 nm and the magnetic layer thickness in the range of 35 to 100 nm with Example 1 as the basic composition. The error rate value (pieces / MB) of the obtained computer tape is shown with each point. As is clear from the figure, it can be seen that the error rate after the endurance running test increases in the lower area in the figure than the line (shown by the solid line) where Dc / Dm is 0.5.

  FIG. 3 shows the results of FIGS. 1 and 2 collectively. It can be seen that the range of Dc and Dm surrounded by the lines of Dc / Dm = 1, Dc / Dm = 0.5, and Dm = 100 nm shows a good range of C / N and durability.

  FIG. 4 shows the relationship between the particle size of the magnetic powder and C / N. The experiment was conducted with Example 1 as the basic composition and the particle size of the magnetic powder varied in the range of 15 to 20 nm. When the particle diameter of the magnetic powder is less than 20 nm, C / N is larger than when the particle diameter of the magnetic powder is 20 nm. It can also be seen that C / N increases as the particle size decreases.

It is a figure which shows the relationship between the value of Dc / Dm, and C / N. It is a figure which shows the relationship between the value of Dc / Dm, and the error rate (ER) after an endurance running test. It is a summary figure which shows the relationship between the value of Dc / Dm, C / N, and ER. It is a figure which shows the relationship between the particle diameter of magnetic powder, and C / N.

Claims (3)

In a magnetic recording medium having a magnetic layer containing at least a magnetic powder having an average particle diameter of 5 nm to 30 nm and carbon black on a nonmagnetic support, the thickness of the magnetic layer is less than 100 nm, and the carbon black When the average particle diameter is less than 100 nm, the axial ratio or plate ratio of the magnetic powder is 1 or more and less than 3, the average particle diameter of the carbon black is Dc, and the thickness of the magnetic layer is Dm. A magnetic recording medium satisfying the relationship of 5 ≦ Dc / Dm ≦ 1.0.   The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 10 nm or more and less than 100 nm.   A magnetic tape cartridge comprising a cartridge case and the magnetic recording medium according to claim 1 incorporated in the cartridge case.

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